Molluscs and Arthropods Diversity: A Guide to Classes and Orders

1. Lab #12 Molluscs and Arthropods

2. Phylum Mollusca • Class Scaphopoda(300 species) • tooth shells, tusk shells • all are burrowing marine animals • most distinctive characteristic – conical shell open at both ends • Class Monoplacophora • undivided arched shell • flat foot • Class Caudofoveata • wormlike molluscs • live in vertical burrows on the deep sea floor • lack a shell or a foot • Class Aplacophora(250 species) • “solenogasters” • lack a shell • may be closely related to the flatworms • most have a radula • surface dwellers on corals • carnivores

3. Class Gastropoda • Gastropod diversity • Subclass Prosobranchia (gill in front of heart): marine snails and abalone • largest group • 20,000 species, mostly marine • few are freshwater and terrestrial • most are herbivores or deposit feeders • some are carnivorous – inject venom into their prey (fishes, other molluscs or annelids) using a modified radula that is shaped like a harpoon abalone

4. Class Gastropoda • Gastropod diversity • Subclass Opisthobranchia (gill in back of heart): sea hares, sea slugs • mostly marine • fewer than 2,000 species • shell, mantle cavity and gills are reduced or may be lost in this group • many species have nematocysts – acquire these from their cnidarian prey • foot may be modified for swimming

5. Class Gastropoda • Gastropod diversity • Subclass Pulmonata • 17,000 species • most are freshwater and terrestrial – snails and slugs • mostly herbivores • long radula for scraping plant material • mantle cavity is highly vascular and serves as a lung – open to the air via a pneumostome

6. Subclass Pulmonata

7. Class Bivalvia = the Clam

8. labial palps anterior adductor muscle

9. foot mantle http://www.youtube.com/watch?v=YKTl5kwtjMc

10. http://iweb.tntech.edu/mcaprio/clam.htm

12. Class Cephalopoda = the squid http://blog.tepapa.govt.nz/2008/04/29/dissection-of-giant-squid/

13. Arthropod Phylogeny • Subphylum Chelicerata: first pair of appendages are pincerlike • Class Merostomata • Class Arachnida • Class Pycnogonida • Subphylum Crustacea: head with two pairs of antennae; biramous appendages • Class Malacostraca • Class Branchiopoda • Class Maxillopoda • Subphylum Hexapoda: body divided into head, thorax and abdomen; uniramous appendages on the thorax • Class Insecta • Subphylum Myriapoda: body divided into a head and trunk; uniramous appendages • Class Diplopoda • Class Chilopoda

14. Phylum Arthropoda • Subphylum Chelicerata: body divided into a prosoma and an opisthosoma; first pair of appendages are pincer-like and used for feeding • Class Merostomata– horseshoe crabs • Class Arachnida– scorpions, spiders, daddy long legs, mites & ticks • Class Pycnogonida – sea spiders

15. Subphylum ChelicerataClass Arachnida • Order Scorpionida: scorpions • tropical to desert climates • are secretive and nocturnal • distinctive chelicerae that surround the mouth + a pair of chelate pedipalps • opisthomais divided into a pre-abdomen and a post-abdomen (called the tail) – curves dorsally and anteriorly over the pre-abdomen when aroused • tip of the tialis the telson with a sting – bulbular base that contains venom-producing glands and a hollow, sharp barb • only a few scorpions are toxic to humans – Androctonus (northern Africa) • - Centuroides(Mexico, Arizona and New Mexico) • reproduction involves a complicated “dance” that lasts several hours • development of a scorpion requires 1.5 years until maturity chelicerae

16. Class Arachnida • Order Opiliones:daddy long legs or harvestman • body appears ovoid (unlike a spider) • many are omnivorous as opposed to carnivorous spiders • Order Acarina:mites and ticks • great impact on human health and welfare • free-living forms are herbivores or scavengers – damage to crops • parasitic forms feed on blood and tissue fluids • some can be permanent ectoparasites • ticks are ectoparasites during the entire life history Acarina Opiliones

17. Class Pycnogonida • sea spiders • all are marine • most common in cold waters • live on the ocean floor • feed on cnidarian polyps and ectoprocts • some feed through sucking tissues through a proboscis

18. Class Arachnida • Order Araneae: 34,000 species of spiders (carnivorous) • prosoma: bears chelicerae with poison glands and fangs • pedipalpsaround the mouth are leglike • are modified in the males for sperm transfer • opisthoma/abdomen: swollen and contains openings to the reproductive tract, book lungs and trachea • end of the opisthoma – spinnerets - associated with silk glands – emits a protein as a liquid that hardens with air as it is drawn out = web for prey capture • bite their prey to paralyze them – puncture the body with their chelicerae and inject venom • suck out the blood first, then inject digestive enzymes to “liquefy” internal organs • few are toxic to humans – Black widow (Lactrodectus) and brown recluse (Loxosceles) • mating involves complex behaviors involving tactile, chemical and visual signals

19. Phylum Arthropoda • Subphylum Crustacea: mostly aquatic; head with two pairs of antennae; one pair of mandibles and two pairs of maxillae; biramous appendages • Class Malacostraca • Class Branchiopoda • Class Maxillopoda

20. Subphylum Crustacea Class Malacostraca = the crayfish

22. 1 – uropods 2 – telson 3 – abdomen 4 – cephalothorax 5 – cephalic groove 6 – walking legs 7 – cheliped 8 – eye 9 – rostrum a - antennae Crayfish dissectionExternal Anatomy

23. Crayfish dissection • 8 paired appendages are present on the cephalothorax • first two pairs = first and second antennae • third through fifth are associated with the mouth – crushing, tearing food • the 3rd pair = mandibles • 4th and 5th = maxillae (#1 and #2) • 6th through the 8th are called the maxillipeds – food handling • last two maxillipeds bear gills antennules (1) antennae (2) mandible (3) second maxillae (4) first maxilliped(5), second maxilliped(6) third maxillipeds (7) walking legs or chelipeds(8) openings to the green glands (9)

24. appendages 9 through 13 are on the thorax – called walking legs (or periopods) • first pair (pair #9) is called the cheliped (4) – chelicera used in defense and capturing food • remaining pairs are for walking/crawling along the sea floor • 1 = uropods • 2 = pleopods or swimmerets • 3 = walking legs or periopods • 4 = cheliped (1st walking leg) • 5 = 1st swimmeret • 6 = antennae

25. appendages 14 through 18 are on the abdomen – called swimmerets or pleopods (2) • 1st pair of swimmeret is larger in the male – for sperm transfer • abdomen is associated with the telson • bears the anus which is flanked on either side by flattened biramous appendages called the uropods (1) • flipperlike structure used for swimming • 1 = uropods • 2 = pleopods or swimmerets • 3 = walking legs or periopods • 4 = cheliped (1st walking leg) • 5 = 1st swimmeret • 6 = antennae

26. in females – eggs attach to the pleopods and the embryos brood on these “legs” until hatching • in males – the first two pleopods (#10 and #11) are modified into gonopodsor claspers for sperm transfer Male Female 1 – swimmeret 2 – seminal receptacle 3 – walking leg #5 4 – walking leg #4 5 – female genital opening 6 – walking leg #2 1 – swimmeret 2 – male genital opening 3 – 1st pair of swimmerets - clasper 4 – 7 – walking legs 8 – base of the first pair of walking legs

27. Male crayfish Male crayfish modified first swimmerets called gonopods (1) openings to each vas deferens (2) third (3), fourth (4) and fifth (5) walking legs

28. swimmerets (1) opening to the seminal receptacle (2) openings to the oviducts (3) third pair of walking legs (4). Note: These openings have been expanded to make them more visible. Female crayfish

29. Crayfish meat abdominal flexor muscles (1) & abdominal extensor muscles (2) = MEAT intestine (3), one of the fifth walking legs (4), carapace (7), uropods (5) and telson (7).

30. Crayfish internal anatomy digestive gland

32. 1 – walking legs 2 – gills 3 – cephalic groove 4 – 3rd pair maxilloped 5 –cheliped 6 – right eye 7 – rostrum 8 – right long antenna

33. Internal anatomy green glands (1) , compound eyes (2), the digestive gland (3), mandibular muscles (4), gills (5), abdominal extensor muscle (6), a portion of the fifth walking leg (7), and one of the third maxillipeds (8).

34. Class Branchiopoda sea monkey • primarily live in freshwater • all possess flattened, leaflike appendages used in respiration, filter feeding and locomotion • order Cladocera: water fleas • e.g. Daphnia • large carapace covers their body • sexual reproduction produces “wintering eggs” that hatch in spring • order Anostraca: fairy shrimp and brine shrimp • fairy shrimp live in temporary ponds that are formed through thaws and rains • eggs are brooded by the female • after the female dies and the pond dries – eggs encyst and enter a dormant stage • with water – hatch into larval stages • dormant embryos can be carried by wind and rain daphnia water flea fairy shrimp

35. Phylum Arthropoda • Subphylum Hexapoda: body divided into head, thorax and abdomen; five pairs of head appendages; three pairs of uniramous appendages on the thorax • Class Insecta • Subphylum Myriapoda: body divided into a head and trunk; four pairs of head appendages; uniramous appendages • Class Diplopoda • Class Chilopoda

36. Subphylum Myriapoda Class Diplopoda • terrestrial • 4 classes – characterized by a body consisting of head and trunk plus uniramous appendages • Class Symphyla • Class Pauropoda • Class Diplopoda: millipedes • Class Chilopoda: centipedes Class Chilopoda

37. Subphylum Myriapoda • Class Diplopoda: millipedes • head with mandibles for chewing + two antennae • circular body with 11 to 100 trunk segments – each segment is actually two segments fused together • two pairs of legs per segment – push against the substrate for locomotion • two ganglia, two pairs of ostia and two tracheal trunks per segment • feed on decaying plant material using mandibles

38. Subphylum Myriapoda • Class Chilopoda: centipedes • nocturnal • head with maxillae and mandibles + 2 antennae + compound eyes or ocelli • flattened body - 15 or more trunk segments each with one pair of legs per segment • first pair of legs modified into forcipules or venom claws • not seen in other arthropods • rest of the legs = maxillopeds • fast-moving predators – small arthropods, earthworms and snails • bite can be annoying to humans

39. Subphylum Hexapoda = Insects

41. Grasshopper External Anatomy

43. Grasshopper Internal Anatomy Dorsal view

44. ovaries Ventral view gastric caecae below the crop Malphigian tubules Tracheae hindgut/intestine ovipositor

46. Subphylum Trilobitomorpha • the fifth, extinct subphylum • trilobites • dominant form of life in the oceans 600 MYA • crawled along the substrate feeding on annelids, molluscs and decaying organic matter • oval body – flattened and divided into three longitudinal regions • all body segments are articular – roll into a ball • appendages – two lobes or rami – called biramous • inner lobe - walking leg • outer lobe bears spikes or teeth – digging or swimming or as gills in gas exchange